Recently, a method for synthesizing a sulfide-based solid electrolyte by reacting Li2S—P2S5 in a polar organic solvent has been suggested as a mass-production process for synthesizing a sulfide-based solid electrolyte. However, since the reaction occurs in the solvent, amorphous particles having heterogeneous spherical shape are obtained as the sulfide-based solid electrolyte. The amorphous solid electrolyte has a small specific surface area, so that a contact area between the solid electrolyte and an electrode active material may be reduced in a composite electrode.
In the related arts, a method of mixing two solvents having different solubilities to sulfur compounds of the electrolyte has been disclosed in order to control microparticles, but is not pertinent to a needle-like sulfide-based solid electrolyte. In addition, a method for finely pulverizing particles by using a milling machine and a temperature-retaining reaction vessel has been disclosed, but the size of the reaction device may be substantially increased in that method.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.